The mystery behind a fallen turbine blade at the Ocotillo Wind power plant east of San Diego has led the manufacturer to curtail operations at select wind farms around the world.

Siemens, a global leader in wind-turbine manufacturing, confirmed Monday that it has convened a team of experts at a wind farm outside the desert town of Ocotillo, where a 170-foot blade broke loose and fell to the desert floor. Residents of Ocotillo noticed the fallen blade on Thursday morning.

“Siemens does not yet know the root cause of this incident and is working to determine if and how this is related to a recent similar incident in Iowa,” the company said in a written statement. “Out of an abundance of caution, Siemens is taking the step of curtailing all turbines with the B53 blade type globally.”

On April 5, a blade broke on the same model turbine at MidAmerican Energy’s 200MW Eclipse wind farm in Iowa’s central Audubon and Guthrie counties.

The B-53 blade type is used on a turbine model with about 700 units in operation worldwide — 600 of those the United States.

The curtailment meant some turbines remained in operation at slower speeds. Ocotillo Wind, an array of more than 90 turbines forming a crescent around the like-named town, remained shut down on Monday, according to Pattern Energy, the developer and operator.

“Each and every turbine is being evaluated,” said Matt Dallas, a spokesman for Pattern, a San Francisco-based wind and transmission developer with offices in La Jolla.

The fallen blade ignited new safety concerns among critics of the plant, who posted photos and videos to the Internet of the crumpled white tube amid sparse desert undergrowth, along with the idled turbine above, missing one of its three arms.

Much of Ocotillo Wind, 70 miles east of the City of San Diego, is on public land overseen by the Bureau of Land Management and remains accessible to hikers and off-road vehicles.

The blade apparently detached during the night — late Wednesday or early Thursday — meaning no one may have seen it break and fall.

The turbine blades at Ocotillo are made of a glass fiber-reinforced epoxy resin and are attached to a rotor suspended about 240 feet from the ground.

San Diego Gas & Electric buys electricity from Ocotillo under a 20-year contract at undisclosed prices. California utilities are ramping up clean-energy production under a state law requiring retailers to provide one-third of electricity from renewable sources by 2020.